NAGMA comes from bicarbonate loss (diarrhoea, fistula, ureteric diversion), renal tubular acidosis, or chloride loading (large volumes of 0.9% saline). The urine anion gap separates GI from renal causes.
At the bedside
Timed steps- 1
Obvious cause?
HistoryDiarrhoea, pancreatic/biliary fistula, ileal conduit, large saline infusions, acetazolamide, recovery phase of DKA.
- 2
Urine anion gap
TestUAG = urine Na+ + K+ − Cl-. Negative (−20 to −50) = appropriate NH4+ excretion (GI loss). Positive = impaired renal acid excretion (distal RTA, CKD).
- 3
RTA
ClassifyType 1 (distal): urine pH > 5.5, hypokalaemia, stones. Type 2 (proximal): bicarbonaturia, Fanconi. Type 4: hyperkalaemia (hypoaldosteronism, diabetes, drugs).
- 4
Cause + bicarbonate
TreatReplace losses with balanced solutions; oral or IV bicarbonate for ongoing losses or RTA; correct K+ before bicarbonate in hypokalaemia.
Calculators for this topic
NAGMA
Step 1 of ~3
Decision: Obvious cause (diarrhoea, saline, fistula)?
Based on Kraut JA, Madias NE. Educational use; follow local protocol.
Evidence
- Kraut & Madias 2010: urine anion gap and RTA classification.
🇮🇳 India notes
- Acute diarrhoeal disease (including cholera) is a common cause of severe NAGMA with hypokalaemia in Indian ICUs, especially in monsoon months.
References
Test yourself
Module quiz · score 70% to complete the module
Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.